1. Field of the Invention
Example embodiments generally relate to a sheet conveyance device, an image reader, and an image forming apparatus, and more particularly, to a sheet conveyance device, an image reader, and an image forming apparatus for feeding sheets.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet) based on image data using electrophotography. Thus, for example, a charger charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the image carrier; the toner image is then transferred from the image carrier onto a sheet; and finally, a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet, thus forming the toner image on the sheet.
Such image forming apparatuses may include an image reader for reading an image on an original document sheet inserted by a user so as to generate image data. For example, the user inserts the original document sheet into the image reader in such a manner that a leading edge of the original document sheet is fed between driving rollers and driven rollers of feed roller pairs, respectively. In other words, a direction in which the feed roller pairs feed the original document sheet is determined based on a direction in and an angle at which the original document sheet contacts nip portions of the feed roller pairs.
The driven rollers of the feed roller pairs include side driven rollers, provided on both side portions of a driven shaft supporting the driven rollers in an axial direction of the driven shaft, and center driven rollers, provided on a center portion of the driven shaft in the axial direction of the driven shaft. The side driven rollers are formed of hard plastic and the center driven rollers are formed of foam rubber, so that the user can sense contact of the original document sheet with the feed roller pairs precisely.
However, when the center driven rollers formed of the foam rubber press against the opposing center driving rollers, the pressure of that contact may deform the center driven rollers. Accordingly, the nip portions formed between the center driven rollers and the center driving rollers may be misaligned with the nip portions formed between the side driven rollers and the side driving rollers in a sub-scanning direction, that is, an original document sheet conveyance direction, as well as in a direction perpendicular to the original document sheet conveyance direction. Consequently, such misalignment of the nip portions may crease the original document sheet conveyed through the nip portions.
Further, in order to reduce creasing of the original document sheet, a bearing for supporting a center portion of a driving shaft supporting the driving rollers in an axial direction of the driving shaft may be shifted downstream in the original document sheet conveyance direction, so as to bend the driving shaft. Accordingly, the nip portions formed between the center driven rollers and the center driving rollers may be misaligned with the nip portions formed between the side driven rollers and the side driving rollers in the sub-scanning direction, that is, the original document sheet conveyance direction. Consequently, when the user inserts the original document sheet into the nip portions and thereby the leading edge of the original document sheet contacts the nip portions, such misalignment of the nip portions may skew the original document sheet. As a result, the image reader may not read an image on the original document sheet properly.